2000 205v. All of a sudden my tach starts at 1900 when off. Makes for some scary readings when underway. Not sure what caused it or of there is an adjustment. Anyone seen this before?

Disconnect the battery, clean the terminals and the ends of any cables that attach to it, as well as any battery switch connections. If that doesn't fix it, call your nearest MC dealer and ask if they have a test rig for the Medallion gauges. This was a required item for MC dealers when your boat was new.